Subsea Intervention

ABSTRACT

A method and system of subsea intervention comprises lowering one or more assemblies of intervention equipment into the sea. Underwater marine units (such as remote operated vehicles or small submarines) may be employed to connect the assemblies to each other and to the subsea wellhead equipment. The subsea wellhead equipment includes a carrier line spool (e.g., coiled tubing spool, wireline spool, slickline spool) and equipment to inject a carrier line from the carrier line spool into the subsea well. The carrier line spool can be located underwater, such as on the sea floor or positioned above the subsea wellhead equipment.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Ser. No. 09/920,896, filed Aug. 2, 2001,which claims the benefit under 35 U.S.C. §119(e) of U.S. ProvisionalApplication Ser. Nos. 60/225,230, filed Aug. 14, 2000; 60/225,440, filedAug. 14, 2000; and 60/225,439, filed Aug. 14, 2000.

BACKGROUND OF INVENTION

Preliminary Amendment—Remarks:

Preliminarily, please consider the following remarks.

The following remarks address prior art rejections asserted againstclaims of the parent application, of which the present application is acontinuation. References as applied against the claims of the parentapplication include Avakov and Moss, as well as other references.

Independent claim 1 is allowable over Avakov. There is no teaching inAvakov of a carrier line spool that is adapted to be positionedunderwater.

The Dec. 1, 2003 Office Action stated that FIG. 1 of Avakov shows thedrum/reel 20 to be lower than the top of the framework 24 of thewellhead, which indicates that the drum/reel 20 is located subsea. Dec.1, 2003 Office Action at 5. It is respectfully submitted that thisassertion of the Office Action is inconsistent with the expressed wordsof Avakov itself, which teaches that the drum/reel is positioned on atruck for mobile operations. Placing the drum/reel 20 subsea wouldcontradict this teaching of Avakov, as the drum/reel 20 would no longerbe mobile.

Also, FIG. 1 of Avakov is a schematic diagram not intended to be toscale. There is no teaching whatsoever that the drum/reel 20 can bepositioned underwater. The assertion made in the Office Action is basednot on any specific teaching of Avakov, but instead is based onspeculation of what FIG. 1 of Avakov might disclose.

It is respectfully submitted that the subject of claim 1 is notdisclosed or suggested by Avakov.

Independent claim 17 is also allowable over Avakov, which fails to teachor suggest “positioning a carrier line spool underwater.”

With respect to the subject matter of independent claim 13, the Dec. 1,2003 Office Action conceded that Avakov does not disclose an underwatermarine unit to operatively couple a carrier line to subsea wellheadequipment. However, the Office Action cited to Moss as teaching thismissing element. However, Applicant notes that Moss does not teach orsuggest the underwater marine unit of claim 13. Claim 13 recites anunderwater marine unit adapted to operatively couple a carrier line tosubsea wellhead equipment. That is not disclosed or suggested at all byMoss. In Moss, an ROV is described as attaching the entire interventionsystem, packaged in the three-dimensional space frame 29, to the subseatree. There is absolutely no need in Moss for an underwater marine unitto couple a carrier line to subsea wellhead equipment. Because neitherAvakov nor Moss teaches the underwater marine unit recited in claim 13,it is respectfully submitted that the combination of Avakov and Mossalso does not teach or suggest the invention.

The Dec. 1, 2003 Office Action asserted that the ROV of Moss “is capableof performing a number of functions beneath the surface of the sea.”Dec. 1, 2003 Office Action at 5. Thus, the Office Action stated that“[i]t is assumed that if the ROV were capable of attaching the entiretyof an intervention system then it would be adapted to able [sic] toattach a carried line to a wellhead frame.” “Id”. This reasoning doesnot support a “prima facie” case of obviousness. As stated by the MPEPitself, the mere fact that references “can be” modified does not renderthe resultant combination obvious unless the prior art also suggests thedesirability of the combination. MPEP §2143.01 (8th ed., Rev. 1) at2100-126. “Although a prior art device may be capable of being modifiedto run the way the apparatus is claimed, there must be a suggestion ormotivation to do so.” “Id”. Except for a conclusory statement that theROV of Moss is capable of doing what is recited in the claim, the Dec.1, 2003 Office Action has failed to cite to any actual teaching orsuggestion in the references of the claimed subject matter.

It is therefore respectfully submitted that claim 13 is not obvious overAvakov and Moss.

Independent claim 28 is also similarly allowable over the assertedcombination of Avakov and Moss.

Independent claim 30 is also allowable over the asserted combination ofMoss and Kogure. As stated in Moss, a goal of its proposed invention isthe elimination of a riser to the surface. Moss, ¶¶ [0012]-[0013].Kogure is directed to a riser that includes a riser stabilizing systemand supplementary buoyancy tanks fixedly positioned to the upper end ofthe riser 16. Kogure, 3:14-18; 3:25-26, 4:31-33. Thus, while Mossteaches the elimination of a riser, Kogure teaches the exact opposite—aspecific type of riser with equipment to support ease of use of theriser. Combining the teachings of Moss and Kogure would defeat the goalsand objective of both references. A basic requirement of establishing a“prima facie” case of obviousness is that a proposed modification cannotrender the prior art unsatisfactory for its intended purpose or changethe principle of operation of a reference.” “Id”. at § 2145 at 2100-156.Therefore, there can be no motivation or suggestion to combine theteachings of Kogure and Moss.

Therefore, claim 30 is not obvious over Moss and Kogure.

All dependent claims are allowable for at least the same reasons ascorresponding independent claims. Allowance of all claims isrespectfully requested.

BACKGROUND OF INVENTION

The invention relates to subsea well intervention.

Subsea wells are typically completed in generally the same manner asconventional land wells and are subject to similar service requirementsas land wells. Further, as with land wells, services performed byintervention can often increase the production from the subsea well.However, intervention into a subsea well to perform the desired servicesis typically more difficult than for land wells. Conventionally, toperform subsea intervention, the operator must deploy a rig (such as asemi-submersible rig) or a vessel, as well as a marine riser, which is alarge tubing that extends from the rig or vessel to the subsea wellheadequipment.

Interventions may be performed for various reasons. For example, anoperator may observe a drop in production or some other problem in thewell. In response, the operator performs an intervention operation,which may involve running a monitoring tool into the subsea well toidentify the problem. Depending on the type of problem encountered, theintervention can further include shutting in one or more zones, pumpinga well treatment into a well, lowering tools to actuate downhole devices(e.g., valves), and so forth.

Although intelligent completions may facilitate the determination ofwhether to perform intervention, they do not offer a complete range ofdesired intervention solutions. In addition, not all wells are equippedwith the technology.

Performing intervention operations with large vessels and heavyequipment such as marine riser equipment, as conventionally done, istypically time consuming, labor intensive, and expensive. Therefore, aneed continues to exist for less costly and more convenient interventionsolutions for subsea wells.

SUMMARY OF INVENTION

In general, according to one embodiment, an apparatus for use with asubsea well comprises subsea wellhead equipment and a carrier line spoolhaving a carrier line and that is positioned underwater. An underwatermarine unit is adapted to attach the carrier line to the subsea wellheadequipment.

Other features and embodiments will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an embodiment of a subsea well system having pluralwells.

FIG. 2 illustrates a completed well in the subsea well system of FIG. 1.

FIG. 3 illustrates an intervention assembly according to one embodimentconnected to subsea wellhead equipment.

FIG. 4 illustrates a sea vessel used for transporting interventionequipment assemblies in accordance with an embodiment.

FIG. 5 illustrates removing a tree cap from the subsea wellheadequipment, in accordance with an embodiment.

FIG. 6 illustrates assembling an intervention assembly to the subseawellhead equipment, in accordance with an embodiment.

FIG. 7 illustrates an intervention assembly according to anotherembodiment connected to subsea wellhead equipment.

FIG. 8 illustrates a carousel system for use with the interventionassembly of FIG. 7.

FIG. 9 illustrates another embodiment of an intervention assembly thatis connected to subsea wellhead equipment.

FIGS. 10-14 illustrate deployment of the intervention assembly of FIG.9.

FIG. 15 illustrates yet another embodiment of an intervention assemblythat uses either slickline or wireline.

FIG. 16 illustrates a variation of the embodiment of FIG. 15.

FIG. 17 illustrates another variation of the embodiment of FIG. 15.

FIGS. 18-23 illustrate a deployment sequence of the embodiment of FIG.15.

FIG. 24 illustrates a further embodiment of an intervention assemblythat employs a subsea tractor capable of moving along a sea floor.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details and that numerous variations ormodifications from the described embodiments may be possible.

As used here, the terms “up” and “down” “upper” and “lower” “upwardly”and downwardly” “below” and “above” and other like terms indicatingrelative positions above or below a given point or element are used inthis description to more clearly describe some embodiments of theinvention. However, when applied to equipment and methods for use inwells that are deviated or horizontal, or when applied to equipment andmethods that when arranged in a well are in a deviated or horizontalorientation, such terms may refer to a left to right, right to left, orother relationships as appropriate.

Referring to FIG. 1, in one example, a subsea field 8 includes aplurality of wells 10 (10A, 10B, 10C, 10D and 10E illustrated). Eachwell 10 includes a wellbore 12 (FIG. 2) that is lined with a casing orliner 14. A tubing 16, such as a production tubing, may be positioned inthe wellbore 12. A packer 18 isolates an annulus region 20 between thetubing 16 and the casing 14 from the rest of the wellbore. Subseawellhead equipment 22 is located at the well surface, which is the seafloor 24.

As further shown in FIG. 1, the wellhead equipment 22 can be connectedto conduits 26 (e.g., hydraulic control lines, electrical control lines,production pipes, etc.) that are run to a subsea manifold assembly 28.Conduits 26A, 26B, 26C, 26D, and 26E connect respective wellheadequipment 22A, 22B, 22C, 22D and 22E to the manifold 28. In turn,various conduits 30 are run to a host platform 32 (which can be locatedat the sea surface, or alternatively, on land). For example, theplatform 32 can be one of many floating facilities, or the platform 32can be a land-based site. The platform 32 collects production fluids andsends appropriate control (electrical or hydraulic) signals or actuatingpressures to the wells 10A-10E to perform various operations. Duringnormal operation, well fluids are delivered through the tubing 16 ofeach well and the conduits 26, manifold 28, and conduits 30 to theplatform 32.

However, over the life of the wells 10, production drops or otheranomalies may be encountered. Typically, sensors may be installed ineach wellbore 12 to monitor various well attributes, such as wellpressure and temperature and production flow rate. Also, formationcharacteristics can be monitored to determine the productivity of theformation. If a drop in production or some other anomaly is detected inthe wellbore 12, an intervention operation may be needed.

With a subsea well, performing an intervention operation usingconventional techniques can be expensive. Typically, a large sea vesselor a rig may have to be transported out to the well site. The large seavessel is needed to haul heavy equipment required to perform theintervention. For example, one such piece of heavy equipment is a marineriser (a relatively large diameter metal tubing) that runs from the seavessel to the subsea wellhead equipment 22.

In accordance with some embodiments of the invention, to provide formore convenient and efficient intervention of subsea wells, remoteoperated vehicles (ROVs), autonomous underwater vehicles (AUVs), smallsubmarines, or other underwater marine units are used to carry some ofthe intervention equipment to a location proximal the subsea wellhead22. The underwater marine units are also capable of connecting orattaching the intervention equipment to the subsea wellhead equipment.By using embodiments of the invention, certain heavy components (e.g.,marine risers) that are conventionally used for intervention operationsmay be omitted so that smaller sea vessels may be employed.

As shown in FIG. 3, in one embodiment, the intervention equipmentincludes a carrier line spool 41 on which a carrier line 44 may beloaded. Examples of carrier lines include coiled tubing, wirelines,slicklines, and so forth. The carrier line spool 41 can be positioned onthe sea floor 24 (as illustrated in FIG. 3), or alternatively, thecarrier line spool 41 can be carried on a sea vessel (as illustrated inFIG. 7). In yet another embodiment, the carrier line spool 41 is part ofa well intervention string that is attached to the subsea wellhead(shown in FIG. 9). The intervention method and apparatus according tosome embodiments allows the carrier line 44 to enter the well withvarious barriers (in the form of sealing rams, as discussed below) inplace to seal wellhead pressure from the sea. Also, the barriers enablea sea vessel to leave the well site at any time (such as due toemergency or mechanical problems) while the seal is maintained by thewellhead equipment.

In the embodiment of FIG. 3, the intervention equipment further includesa gooseneck 42 to support and guide the carrier line 44. The gooseneck42 is attached to an injector head 34 that forces the carrier line intoor out of the wellbore 12. The injector head 34 includes a drivemechanism (e.g., a chain-type drive mechanism) that is capable ofgripping the carrier line 44. The drive mechanism is powered by ahydraulic or electrical motor to drive the chains of the drivemechanism. To protect the components of the injector head 34, theinjector head 34 can be placed in a protective chamber (not shown) thatis filled with a fluid compensated for seawater pressure, or by way of aone atmosphere can. To keep seawater out of this chamber, strippers maybe placed above and below the chamber where the carrier line 44 entersand exits, respectively.

The intervention equipment also includes a blow-out preventer (BOP) 36having rams for sealing around the carrier line 44 to prevent the escapeof well fluids. If wireline or slickline is employed, other types oframs may be used. A lower riser 38 (which is basically a pipe or tubing)is connected below the BOP 36. In another embodiment, the lower riser 38can be omitted.

Attached to the lower end of the riser 38 is an emergency disconnectpackage 40 that is releasably connected to a lower riser package 54. Thelower riser package 54 is connected to the tree structure of the subseawellhead equipment 22. Lower riser packages 54 and emergency disconnectpackages 40 may be readily available from various manufacturers.Typically, the lower riser package 54 includes a connector to attach tothe tree structure of the subsea wellhead equipment as well as an upperprofile to connect to the emergency disconnect package. The lower riserpackage 54 can also include rams that are capable of sealing on orcutting coiled tubing or other types of carrier lines. More generally, aconnector assembly is used to connect the injector head 34 to the subseawellhead equipment. In the illustrated embodiment, the connectorassembly includes the riser 38, emergency disconnect package 40, and alower riser package 54. In other embodiments, other types of connectorassemblies can be used.

Referring to FIGS. 4-6, a method and apparatus of transportingintervention equipment according to the embodiment of FIG. 3 to thesubsea well site and connecting the intervention equipment to the subseawellhead equipment is illustrated. In FIG. 4, a sea vessel 110 is usedto transport a carrier line (e.g., coiled tubing) spool assembly 106, aninjector head/BOP/riser assembly 100, a lower riser package assembly102, and one or more underwater marine units 104 to the well site. Inaddition to the respective intervention equipment tools, each of theassemblies 100, 102, and 106 includes buoyancy tanks to aid the loweringof tools into the sea by the underwater marine units 104. Once the seavessel is located generally over the well in which intervention is to beperformed, the underwater marine units 104 are used to carry the variousassemblies proximal the subsea wellhead equipment 22.

As shown in FIG. 5, a first underwater marine unit 104A carries a treecap removal tool 112 to the subsea wellhead equipment 22. The upper endof the wellhead equipment 22 has a tree cap 114 attached to cover theinner components of the subsea wellhead equipment. To enable theattachment of the intervention equipment to the wellhead equipment, thetree cap 114 is first removed. In accordance with some embodiments ofthe invention, this is accomplished by using a tree cap removal tool 112carried by the underwater marine unit 104A.

The underwater marine unit 104A is attached to an umbilical line 116,which is used to deliver control signals to the underwater marine unit104A. The umbilical line 116 includes electrical wires to deliver powerand signals to navigate the underwater marine unit 104A. Optionally, theumbilical line 116 may also contain hydraulic conduits to providehydraulic power and control. In one embodiment, the umbilical line 116extends from the sea vessel 110 (FIG. 4). Alternatively, the umbilicalline 116 extends from the platform 32 (FIG. 1), which can be a platformat the sea surface or on land.

The underwater marine unit 104A includes an arm 118 that is used tocarry the tree cap removal tool 112. The tree cap removal tool 112 iscarried from the sea vessel 110 to the subsea wellhead equipment.Alternatively, the tree cap removal tool 112 may already be stored in anunderwater storage station, such as one described in copending U.S.patent application Ser. No. 09/921,026, entitled “Subsea InterventionSystem,” to Thomas H. Zimmerman et al., filed on Aug. 2, 2001, which ishereby incorporated by reference. Also, as further described in theincorporated reference, the underwater marine unit 104A may be operatedwithout the umbilical line 116. Instead, an alternative guidance systemis employed. The alternative guidance includes the underwater marineunit 104A guiding itself between underwater points based on laser lightsor underwater tracks. A point can be the underwater storage station andanother point can be the subsea wellhead equipment. Alternatively, theunderwater marine unit 104A is controlled using acoustic wave signals orlong wavelength optical signals (e.g., blue-green laser) communicatedthrough water.

The underwater marine unit 104A carries the tree cap removal tool 112 tothe tree cap 114, with the arm 118 moving the tree cap removal tool 112to a position to engage the tree cap 114. The tree cap removal tool 112causes disconnection of the tree cap 114 from the subsea wellheadequipment 22. The tree cap removal tool 112 is used to bleed off anypressure below the cap 114. Alternatively, bleeding off pressure can beaccomplished via an umbilical line (not shown) from the subsea wellheadequipment below the cap 114. The cap retrieval tool 112 is equipped witha jacking capability for dislodging the cap 114 from the tree of thesubsea wellhead equipment 22. Once the tree cap 114 is removed,attachment of intervention equipment to the subsea wellhead equipment 22can proceed.

In an alternative embodiment, instead of a tree cap, the subsea wellheadequipment can include a valve to perform fluid control. The valve isnormally closed, but can be opened if attachment of interventionequipment to the subsea wellhead equipment is desired. To provide fullbore access for intervention tools, the valve can be a ball valve.

In FIG. 6, the various intervention equipment components according tothe embodiment of FIG. 3 are lowered into the sea to the proximity ofthe subsea wellhead equipment 22. As shown in FIG. 6, the carrier linespool 41 has already been run to the sea floor 24 by an underwatermarine unit 104. The carrier line spool 41 is part of the carrier linespool assembly 106 carried on the sea vessel 112 (FIG. 4). Due to thepossibly heavyweight of the carrier line spool 41, buoyancy tanks (notshown) that are part of the carrier line spool assembly 106 are attachedto the carrier line spool 41 for lowering from the sea vessel 110 by anunderwater marine unit 104. Alternatively, the carrier line spool 41 mayalready have been left at the sea floor 24 proximal the subsea wellheadequipment 22 as part of the well completion procedure.

The other assemblies 100 and 102 similarly include buoyancy tanks. Asshown in FIG. 6, the lower riser package assembly 102 includes the lowerriser package 54 and buoyancy tanks 50 attached by a frame 122 to thelower riser package 54. The injector head/BOP/riser assembly 100includes buoyancy tanks 52 connected by a frame 126 to the assembly. Theassembly 100 includes the gooseneck 42, injector head 34, BOP 36, lowerriser 38, and emergency disconnect package 40. Since the assembly 100 islarger and heavier than the assembly 102, larger buoyancy tanks 52 maybe used.

The lower riser package assembly 102 is carried into the sea by anunderwater marine unit 104B (having an arm 118B), and the injectorhead/BOP/riser assembly 100 is carried by an underwater marine unit 104C(having an arm 118C). The underwater marine units 104B, 104C areconnected by respective umbilical lines 130, 132 to the sea vessel 110(or alternatively, to the platform 32 of FIG. 1). In an alternativeembodiment, instead of using multiple underwater marine units 104B,104C, a single underwater marine unit can be used to carry theassemblies 100 and 102 into the sea in separate runs.

Under control of signals communicated over the umbilical lines 130, 132,or other signaling mechanisms (wired or wireless), the underwater marineunits 104B, 104C attach the lower riser package 54 to the subseawellhead equipment 22. After the lower riser package 54 has beenattached, the buoyancy tanks 50 are detached from the lower riserpackage 54 and carried away by the underwater marine unit 104B.

Next, the underwater marine unit 104C connects the emergency disconnectpackage 40 (at the lower end of the assembly 100) attached at the lowerend of the riser 38 to the lower riser package 54. After connection, thebuoyancy tanks 52 are detached from the assembly 100 and carried away bythe underwater marine unit 104C.

The underwater marine units 104B and 104C (as well as the unit 104A) canbe driven back to the sea vessel 110 (or the platform 32).Alternatively, the underwater marine units 104 can be kept in closeproximity to the subsea wellhead equipment 22 that is subject tointervention in case some further manipulation of the interventionequipment is needed. Although plural underwater marine units 104A, 104B,and 104C are described, a smaller (or greater) number of underwatermarine units may be employed in further embodiments.

In an alternative embodiment, the gooseneck 42, injector head 34, BOP36, riser 38, emergency disconnect package 40, and lower riser package54 can be lowered as a single assembly (instead of separate assemblies).This reduces the number of attachment operations needed to be performedunderwater by the underwater marine units 104.

To address various handling issues, the intervention equipment (ormodules of the intervention equipment) may be assembled at a shallowdepth near the sea vessel 110. After assembly in the shallow depth, theassembly can be tested before lowering to the sea floor. Duringassembly, buoyancy tanks may be connected to the riser 38 to place it intension to reduce bending stresses on the riser 38 and stresses onconnections.

Umbilical lines 142 and 144 for intervention control and pumpingoperations may be lowered from the sea vessel 110 for connection to thesubsea wellhead equipment 22 and the injector head 34. As further shownin FIG. 3, if the carrier line spool 41 is a coiled tubing spool, then acoiled tubing flow control line (not shown) can be run from the seavessel 110 for connection to a connector 140 of the spool 41. Instead ofbeing run from the sea vessel 110, the umbilical lines and coiled tubingflow line can be run from the host platform 32 (FIG. 1). The latterapproach reduces the amount of hydraulic and pumping equipment needed onthe sea vessel 110. In yet another approach, a manifold (such asmanifold 28 in FIG. 1) provided on the sea floor 24 can be used toconnect to the umbilical lines and coiled tubing flow line. The coiledtubing flow line connects a source of fluid to the subsea wellheadequipment 22. Alternatively, if the spool 41 is a wireline spool, thenan electrical cable can be run from the sea vessel 110 or other sourceto connect to the spool 41.

To provide structural rigidity to each intervention equipment assembly(100 or 102), a frame or other structure (not shown) may be connectedaround the assembly. The frame provides stiffness to the assembly toprotect components from undue bending stresses. The frame can also carrybuilt-in buoyancy tanks. Further, the frame may include aself-propulsion mechanism to help an underwater marine unit 104transport the assembly to a desired underwater location. The frame mayalso be used as a platform that can be towed behind the sea vessel 110.The intervention equipment can be kept on the frame and not loaded ontothe sea vessel 110.

After connection of the intervention equipment to the wellhead equipment22, the assembly illustrated in FIG. 3 is provided. As further shown inFIG. 2, the carrier line 44 deployed by some embodiments of theinvention through subsea wellhead equipment 22 is connected to anintervention tool 150. As examples, the intervention tool 150 may be amechanical, hydraulic, or electrical actuator used for operating variousdownhole devices (e.g., valves). Alternatively, the intervention tool150 includes sensors or monitors used for collecting measurementsregarding various well attributes (e.g., temperature, pressure, etc.).

In one embodiment, to switch intervention tools, the carrier line 44 israised into the riser 38. The emergency disconnect package 40 is thenunlatched from the lower riser package 54, with the equipment above theemergency disconnect package 40 raised to the surface (the sea vessel110) or to a point in the sea high enough for underwater marine units104 or divers to switch out tools. Once raised to such a point, thecarrier line 44 is lowered out of the riser 38 so that switching of theintervention tool can be performed (in which the present tool isdisconnected from and a new tool is attached to the carrier line 44).

In addition to various intervention operations, the equipment discussedabove may also be used to carry a drilling string into a well to performsubsea drilling operations. Further, installment of spooled tubing,spooled completions, and spooled velocity strings into a well can beperformed.

Referring to FIG. 7, in an alternative embodiment, the carrier linespool 41 is located on the sea vessel 110 instead of the sea floor 24.In this alternative arrangement, one or more assemblies containing aninjector head 200, BOP 202, riser 204, emergency disconnect package 206,and lower riser package 208 are lowered into the sea for assembly andconnection to the subsea wellhead equipment 22. Since the carrier linespool 41 is located on the vessel 110 (above the injector head 200), agooseneck may not be needed. In yet another arrangement, the injectorhead 200 can be located on the sea vessel 110 instead of in the sea tofurther reduce the number of components that need be lowered to thesubsea wellhead equipment 22.

If a vertical run of the carrier line 44 from the sea vessel 110 to thesubsea wellhead equipment 22 is desired, then the sea vessel 110 mayneed a dynamic positioning system to maintain the sea vessel 110substantially over the wellhead equipment 22. Alternatively, spooling ofthe carrier line 44 at a non-vertical angle from the sea vessel 110 maybe possible, so that dynamic positioning of the sea vessel 110 is notnecessary.

To further enhance convenience, a carousel system 210 according to oneembodiment can be used to enable easy exchanging of intervention toolsattached to the carrier line 44 without retrieving the carrier line 44all the way back to the sea vessel 110. As further shown in FIG. 8, thecarousel system 210 has a rotatable structure 214 with a number ofchambers 212 each containing a respective intervention tool. Therotatable structure 214 is rotatable about an axis 216. Thus, dependingon the desired type of intervention tool, the rotatable structure 214 isrotated so that the appropriate chamber 212 is aligned with the riser204. The carrier line 44 is then lowered into the chamber for engagementwith the tool in the chamber 212.

In operation with the embodiment of FIG. 7, the injector head 200, BOP202, riser 204, a carousel system 210, emergency disconnect package 206,and lower riser package 208 are lowered and attached to the subseawellhead equipment 22. The carousel system 210 is actuated so that theappropriate one of the chambers 212 is aligned with the riser 204. Thecarrier line 44 is then lowered into the chamber 212, where the carrierline 44 engages the tool. Further downward movement of the carrier line44 causes the tool to be run into the wellbore.

After the first intervention operation has been completed, the carrierline 44 is raised. The intervention tool connected at the end of thecarrier line 44 is raised into the corresponding chamber 218 of thecarousel system 210, where the intervention tool is unlatched from thecarrier line 44. The carrier line 44 is raised out of the carouselsystem 210, following which the carousel system 210 is actuated and therotatable structure 214 rotated so that another chamber 212 containinganother type of intervention tool is aligned with the riser 204. Thecarrier line 44 is again lowered into chamber 212, where it engages thenext intervention tool. Another intervention operation is thenperformed. This process can be repeated until all desired interventionoperations possible with tools contained in the carousel system 210 havebeen performed.

In a further embodiment, the carousel system 210 can also be used withthe intervention equipment arrangement shown in FIG. 3.

Referring to FIG. 9, an intervention assembly 300 in accordance withanother embodiment is illustrated. The intervention assembly 300includes a BOP 304 that is connected to subsea wellhead equipment 302.Connected above the BOP 304 is a carousel system 306, in which a numberof intervention tools for selective attachment to a carrier line loadedon a carrier line spool assembly 308. The spool assembly 308 includes aspool 314 on which the carrier line is mounted. The spool assembly 308also includes an injector head 316 that is attached above the carouselsystem 306.

As shown, an underwater marine unit 310 is attached to the spoolassembly 308. The underwater marine unit 310 is attached by an umbilicalline 320 to another entity, such as a sea surface platform, sea vessel,or some other unit (whether located at the sea surface, on land, or onthe sea bottom). In one arrangement, the underwater marine unit 310 iscapable of controlling actuation of the spool assembly 308 in responseto commands communicated over the umbilical line 320. Alternatively,instead of an umbilical line 320, the underwater marine unit 310 isresponsive to a wireless form of signaling, such as acoustic wavesignaling.

Thus, in the embodiment shown in FIG. 9, the carrier line spool assembly308 is attached to the string making up the intervention assembly 300.This is in contrast to the intervention assembly of FIG. 3 or FIG. 7,where the carrier line spool assembly is separate from the interventiontool assembly (with the carrier line spool assembly located either atthe sea bottom as shown in FIG. 3, or on a sea vessel, as shown in FIG.7). One advantage offered by the embodiment of FIG. 9 is that the entireassembly 300 can be carried by the underwater marine unit 310 to thesubsea wellhead equipment 302 as a unit, thereby avoiding multiple runswith underwater marine units to the subsea wellhead equipment, which cantake up a lot of time.

Deployment of the intervention assembly 300 is illustrated in FIGS.10-14. FIG. 10 shows a plurality of subsea wellhead equipment 302A,302B, and 302C, which are connected to a manifold 330 over respectiveflow lines 332A, 332B, and 332C. The manifold 330 is connected byanother flow line 334 to a platform 336, which can be located on land orat the sea surface. As shown in FIG. 10, each of the subsea wellheadequipment 302A, 302B, and 302C are initially covered by a respectivetree cap 338A, 338B, and 338C.

When intervention of the wellbore associated with the subsea wellheadequipment 302C is desired, the tree cap 338C is removed, as shown inFIG. 11. Removal of the tree cap can be accomplished by using anunderwater marine unit. After the tree cap is removed, the interventionassembly 300 is carried by the underwater marine unit 310 to a region inthe proximity of the subsea wellhead equipment 302C, as shown in FIG.12. There, the underwater marine unit is controlled from a remotelocation to engage the assembly 300 with the subsea wellhead equipment302C. Once engaged, as shown in FIG. 13, the intervention assembly 300is ready for operation.

The intervention assembly 300 can be operated as shown in FIG. 13, wherethe underwater marine unit 310 remains attached to the carrier linespool assembly 308. Signaling is communicated over an umbilical line, inacoustic waves, by blue/green laser, or by some other mechanism to theunderwater marine unit 310, which responds to the signaling by actuatingthe signal assembly 308. Alternatively, as shown in FIG. 14, theunderwater marine unit 310 is detached from the spool assembly 308 oncethe assembly 300 is connected to the subsea wellhead equipment 302C. Asfurther shown in FIG. 14, a gooseneck 340 allows the carrier linecarried by the spool 314 to be guided into the injector head 316, wherethe carrier line is attached to one of the intervention tools of thecarousel system 306.

Referring to FIG. 15, another embodiment of an intervention assembly 400is illustrated. In the embodiment of FIG. 15, the carrier line used caneither be a slickline or a wireline. The intervention assembly 400includes a cap adapter 404 for attachment to subsea wellhead equipment402. Attached above the cap adapter 404 is a BOP 406, which in turn isconnected to a lower end of a lubricator 408. The lubricator 408 has alength that is sufficiently long to enable a tool string to bepositioned within the lubricator 408. The intervention assembly 400 alsoincludes a winch or spool 410 on which is mounted either a slickline ora wireline (“carrier line 412”). The carrier line 412 is extended fromthe winch 410 to upper sheaves 414, which direct the carrier line 412into the lubricator 408. In the example shown in FIG. 15, the toolstring in the lubricator 408 includes a tool 416 and weights 418, withthe weights 418 used to help run the tool string into the wellborebeneath the subsea wellhead equipment 402.

In the example of FIG. 15, the winch 410 is driven by an underwatermarine unit 420 that has a drive mechanism 422. When the underwatermarine unit 420 is coupled to the intervention assembly 400, the drivemechanism 422 is operably engaged with the winch 410 to enable the drivemechanism 422 to rotate the winch 410 to either unwind or wind thecarrier line 412. The underwater marine unit 420 is coupled by anumbilical line 424 to a remote entity. The remote entity is capable ofsending commands to the underwater marine unit 420 to operate the winch410.

In the embodiment shown in FIG. 15, the lubricator 408 has a port 426that is capable of being engaged with a corresponding port 428 of theunderwater marine unit 420. Thus, the underwater marine unit can beoperated to dock the port 428 to the port 426. When the ports 426 and428 are docked, the drive mechanism 422 is coupled to the winch 410 inone of three possible ways: electrically, mechanically, and/orhydraulically.

Referring to FIG. 16, in accordance with an embodiment that is avariation of the FIG. 15 embodiment, the subsea wellhead equipment 402is coupled by control lines 430 to a remote location. The control lines430 are used to communicate electrical signals and/or hydraulicpressure. The electrical signals carried by the control lines 430 canprovide power and commands to the intervention assembly 400. In theexample of FIG. 16, the underwater marine unit 420 is also coupled bythe umbilical line 424 to a remote entity.

In yet another variation, as shown in FIG. 17, the underwater marineunit 420 of FIG. 16 is replaced with another type of underwater marineunit 450, which is not coupled by an umbilical line to a remote entity.Instead, the underwater marine unit 450 includes a telemetry interface452 that is capable of communicating wireless signals 454 with theremote entity. In one example, the wireless signals 454 are in the formof acoustic wave signals. Alternatively, the wireless signals can be inthe form of blue/green lasers that carry signals to and from theunderwater marine unit 450. Use of optics in an underwater environmentis feasible with blue/green lasers, since they have relatively longwavelengths. The wireless underwater marine unit 450 can be used in theembodiment of FIG. 17 due to the presence of the control lines 430 thatare coupled to the subsea wellhead equipment 402. In this configuration,power for the winch 410 can be provided over the control lines 430.

Referring to FIGS. 18-23, deployment of the subsea intervention assembly400 of FIG. 15 according to one embodiment is illustrated. As shown inFIG. 18, a sea vessel 500 is brought to a location generally above thesubsea wellhead equipment 402. The underwater marine unit 420 is thendropped from the sea vessel 500 into the sea, where it is driven to aregion in the proximity of the subsea wellhead equipment 402. Theumbilical line 424 connected to the underwater marine unit 420 isspooled from an umbilical line spool 502 that is located on the seavessel 500. As shown in FIG. 19, the sea vessel 500 also includes a liftline spool assembly 504 that is used to deploy a lift line 506. The liftline 506 is lowered into the sea down to the subsea wellhead equipment.The underwater marine unit 420 is then operated to engage the lift line506 to a cap 508 of the subsea wellhead equipment 402. The cap 508 isreleased from the subsea wellhead equipment 402, which may be performedby the underwater marine unit 420, and the lift line 506 is raised bythe lift line spool 504 until the cap 508 is retrieved to the sea vessel500.

As shown in FIG. 20, the BOP 406 and attached cap adapter 404 arelowered by the lift line 506 from the sea vessel 500 into the sea to aregion in close proximity to the subsea wellhead equipment 402. Theunderwater marine unit 420 then guides the cap adapter 404 intoengagement with the subsea wellhead equipment 402 (with the tree cap 508already removed). After performing a test of the engagement of the capadapter 404 to the subsea wellhead equipment 402, the underwater marineunit 420 releases the lift line 506 from the BOP 406.

Next, as shown in FIG. 21, the lubricator 412 is attached to the liftline 506 and lowered into the sea until it reaches right above the BOP406. The underwater marine unit 420 then attaches the lubricator 412 tothe BOP 406. After a successful test, the underwater marine unit 420detaches the lift line 506 from the lubricator 412.

As shown in FIG. 22, in another embodiment, the lubricator 412, BOP 406,and cap adapter 404 can be lowered as an assembly on the lift line 506.Once the assembly 400 is in close proximity with the subsea wellheadequipment 402, the underwater marine unit 420 attaches the cap adapter404 to the subsea wellhead equipment 402. This alternative embodiment ispossible if the lift line assembly 504 is able to support the weight ofthe assembly 400. In some cases, the weight of the assembly 400 can bereduced by attaching buoyancy tanks to the assembly 400.

As shown in FIG. 23, once the assembly 400 is connected to the subseawellhead equipment 402, the underwater marine unit 420 is docked to theport 426 of the lubricator 412. At this point, operation of theintervention assembly 400 can begin.

FIG. 24 shows yet another embodiment of an underwater marine unit 600that is used to deploy an intervention assembly 602. In this embodiment,the underwater marine unit 600 is in the form of a subsea tractor thatis capable of being driven along the sea bottom. The subsea tractor 600includes a lift frame 606 that is pivotable about a pivot element 608.During transport, the lift frame 606 lies horizontally on the upperplatform 610 of the subsea tractor 600.

The subsea tractor 600 also includes a carrier line spool 612 on which acarrier line 614 is mounted. The intervention assembly 602 includes agooseneck 616 that is attached to the lift frame 606. The remainder ofthe intervention assembly 602 can also be attached to the lift frame606.

In operation, the subsea tractor 600 is driven to a location near thesubsea wellhead equipment 620. The subsea wellhead equipment 620 isconnected by several control lines 622 to communicate power and controlsignaling and hydraulic pressure. The lift frame 606 is pivoted along anarcuate path 604 until it reaches an operational position, which isshown in FIG. 24. In this position, the intervention assembly 602 can bemoved into engagement with the subsea wellhead equipment 620. Onceengaged, the carrier line spool 612 can be operated to wind or unwindthe carrier line so that an intervention tool can be lowered through thesubsea wellhead equipment into a wellbore.

A convenient method and mechanism is thus provided to perform subseaintervention. By using underwater marine units inside the sea to connectintervention equipment to subsea wellhead equipment, relatively largesea vessels can be avoided since certain components, such as marinerisers, can be omitted. Also, by positioning a carrier line spool at thesea floor or at some other location inside the sea, a carrier line canbe more conveniently attached to the subsea wellhead. Convenientswitching of intervention tools underwater is also possible by use of acarousel system that has plural chambers containing plural respectivetools.

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover such modifications and variations as fall within the truespirit and scope of the invention.

1. An apparatus for use with a subsea well, comprising: a carrier linespool having a carrier line that is adapted to be positioned underwater;and a stack in a structure separate from the carrier line spool, thestack adapted to operatively couple to subsea wellhead equipment, andthe carrier line attached to the stack.
 2. The apparatus of claim 1,wherein the carrier line spool comprises a coiled tubing spool.
 3. Theapparatus of claim 1, wherein the carrier line spool is selected fromthe group consisting of a wireline spool and slickline spool.
 4. Theapparatus of claim 1, wherein the carrier line spool is adapted to bepositioned on the sea floor separate from the stack.
 5. The apparatus ofclaim 1, wherein the carrier line spool comprises a coiled tubing spool,the apparatus further comprising an injector head adapted to drivecoiled tubing from the coiled tubing spool.
 6. The apparatus of claim 5,wherein the stack comprises the injector head.
 7. The apparatus of claim6, wherein the stack further comprises a gooseneck to provide supportfor coiled tubing reeled from the coiled tubing spool.
 8. The apparatusof claim 5, further comprising at least one buoyancy tank attached to anassembly containing the injector head.
 9. The apparatus of claim 1,further comprising a carousel containing a plurality of interventiontools.
 10. The apparatus of claim 9, wherein the carousel is rotatableunderwater to enable switching of tools for connection to the carrierline.
 11. The apparatus of claim 1, wherein the stack contains anemergency disconnect package.
 12. The apparatus of claim 11, furthercomprising a connector connected between the emergency disconnectpackage and the subsea wellhead equipment. 13-14. (canceled)
 15. Anapparatus for use with a subsea well, comprising: a carrier line spoolhaving a carrier line that is adapted to be positioned underwater and tobe operatively coupled to subsea wellhead equipment; and an underwatermarine unit adapted to operatively couple the carrier line to the subseawellhead equipment, wherein the underwater marine unit comprises aninterface to receive wireless signals.
 16. The apparatus of claim 15,wherein the wireless signals comprise acoustic wave signals.
 17. Amethod of intervention with a subsea well, comprising: positioning acarrier line spool underwater; attaching a stack to subsea wellheadequipment, the stack in a structure separately located from the carrierline spool; and coupling a carrier line of the carrier line spool to thestack.
 18. The method of claim 17, wherein coupling the carrier linecomprises coupling the carrier line to an injector head in the stack.19. The method of claim 18, wherein coupling the carrier line comprisescoupling the carrier line through a gooseneck to the injector head. 20.The method of claim 17, further comprising lowering the carrier lineinto the subsea well to perform an intervention operation.
 21. Themethod of claim 20, further comprising raising the carrier line afterthe intervention operation is completed and switching tools connected tothe carrier line.
 22. The method of claim 21, wherein switching toolscomprises actuating a carousel system having chambers containing aplurality of tools.
 23. The method of claim 22, further comprisingengaging the carrier line with another tool after actuating the carouselsystem.
 24. The method of claim 17, further comprising attachingintervention equipment separate from the carrier line to the subseawellhead equipment.
 25. The method of claim 17, further comprising usingan underwater marine unit to couple the carrier line to the subseawellhead equipment.
 26. The method of claim 17, further comprisinglowering, using an underwater marine unit, the carrier line spool to aposition on a sea floor.
 27. The method of claim 26, further comprisingattaching buoyancy tanks to the carrier line spool to enable theunderwater marine unit to carry the carrier line spool underwater. 28.(canceled)
 29. A method of intervention with a subsea well, comprising:positioning a carrier line spool underwater; coupling a carrier line ofthe carrier line spool to subsea wellhead equipment; using an underwatermarine unit to couple the carrier line to the subsea wellhead equipment;and communicating commands to the underwater marine unit using wirelesssignals.
 30. A subsea intervention method for use with subsea wellheadequipment, comprising: assembling modules containing interventionequipment; and connecting, using an underwater marine unit, theassembled intervention equipment to the subsea wellhead equipment; andattaching one or more buoyancy tanks to at least one of the modules. 31.The method of claim 30, further comprising attaching one or morebuoyancy tanks to the assembled intervention equipment.
 32. The methodof claim 30, wherein assembling the modules comprises assembling acarrier line spool as part of the intervention equipment.
 33. Theapparatus of claim 1, further comprising an underwater marine unit toattach intervention equipment separate from the carrier line to thesubsea wellhead equipment.
 34. The apparatus of claim 1, wherein theintervention equipment includes the stack.